The present invention relates to a flying-type composite magnetic head for use in a magnetic disk drive in such a manner that it is slightly floating over a magnetic recording medium, and more particularly to a flying-type composite magnetic head having not only excellent recording-reproduction characteristics but also good flatness in its air-bearing surface.
As magnetic heads used for writing and reading information in magnetic disk apparatuses, flying magnetic heads as shown in U.S. Pat. No. 3,823,416 and Japanese Patent Publication No. 57-569 are widely used. Such a flying magnetic head is constituted by a slider, a tail end of which is provided with a magnetic gap and the overall slider body is constituted by an oxide-type magnetic material with high permeability.
The flying-type magnetic head is in light contact with a magnetic disk by a spring force when the magnetic disk is stationary, but when the magnetic disk is rotating, a flow of air over the magnetic disk exerts an upward force to a lower surface of the slider, whereby the magnetic head floats over the magnetic disk. When the magnetic disk starts to rotate or stops, the magnetic head comes into sliding contact with the magnetic disk. The contact condition of the magnetic head with the magnetic disk when the magnetic disk is stopped will be explained in detail. First, the flow of surface air becomes gradually slow when the rotation speed of the magnetic disk is reduced. When the magnetic head loses its floating force, it collides with the disk surface and jumps up by its reaction and then falls onto the disk surface again. Such movement is repeated and the magnetic head slides on the disk to finally stop. Accordingly, the magnetic head should withstand shocks at the time of start and stop, and such characteristics are sometimes called CSS characteristics (Contact start stop characteristics).
Flying-type magnetic heads are generally constituted by ferrite which is an oxide-type magnetic material with high permeability have relatively good CSS characteristics. However, the ferrite has a small saturation magnetic flux density, so that sufficiently high recording densities cannot be achieved to recording media having high coercive forces. Specifically, even with use of a Mn-Zn ferrite having a relatively high saturation magnetic flux density Bs, its Bs is at most 5000 G or so.
It was then found that to achieve Bs of 8000 G or more, a magnetic head is desirably provided with a thin magnetic metal layer in its magnetic gap. For instance, Japanese Patent Laid-Open No. 58-14311 proposes a flying-type magnetic head composed of ferrite and provided with a magnetic metal layer with high saturation magnetic flux density only in a magnetic gap portion thereof. However, in this magnetic head, a magnetic transformation part has large inductance after provided with coil windings, so that it has low resonance frequency. This means that it is disadvantageous in recording and reproducing at high frequency. Here, the large inductance is due to the fact that the overall magnetic head is composed of a magnetic material. Accordingly, to achieve low inductance, a magnetic circuit should be made small. From this point of view, U.S. Pat. No. 3,562,444 discloses a flying-type composite magnetic head in which a magnetic core is embedded in and fixed to a non-magnetic slider, without constituting the entire magnetic head with a magnetic material.
Further, the present inventors proposed in Japanese Patent Laid-Open No. 61-199219 a flying-type magnetic head in which a magnetic core is embedded in a non-magnetic slider.
It has been found from the above that to obtain a flying-type composite magnetic head having good recording characteristics to high-coercive force recording media and small inductance, a composite magnetic core should be constituted by a Mn-Zn ferrite substrate with a high saturation magnetic flux density Bs and coated with a thin magnetic layer having high Bs in its magnetic gap portion. Such a magnetic core should then be embedded in a non-magnetic slider. An example of such magnetic heads is shown in Japanese Patent Laid-Open No. 60-154310 by the present inventors.
Further, Japanese Patent Laid-Open No. 61-199217 proposed a magnetic head in which a magnetic gap portion of a magnetic core is in an X-shape. However, this magnetic core having an X-shaped magnetic gap is disadvantageous in that it provides low reproduced output as explained below in detail. As a result of research on the cause of low reproduced output, it has been found that large strain is generated in a high Bs magnetic layer in the process of glass bonding as explained in detail below, resulting in extreme deterioration of the desired characteristics.
Belief of an internal stress generated in a high Bs magnetic layer may be achieved by reducing a thickness of the thin magnetic layer. However, in the magnetic gap structure proposed in Japanese Patent Laid-Open No. 61-199217, a track width and a layer thickness cannot be determined independently. Accordingly, to achieve a certain track width, the thin magnetic layer should inevitably have a larger thickness to some extent.
To eliminate such problems, a gap portion may have a structure in which a relatively thin, high Bs layer is provided in parallel with the gap.
However, in such a structure, undulation takes place in the frequency characteristics of reproduced output due to a so-called "pseudo-gap effect," since the boundary surface between the magnetic thin layer and the ferrite substrate is parallel with the magnetic gap. To prevent this undulation phenomena due to the pseudo-gap effect, a simple structure of a high Bs layer provided in parallel with the magnetic gap line is inappropriate. Further, because of various factors in production, the undulation has not been able to be prevented completely.
Thus, the desired characteristics of a magnetic head for use with a magnetic disk are (1) sufficient recordability to high-coercive force media, (2) low inductance, (3) high reproduced output without causing undulation due to extreme strain in a high Bs magnetic layer, and (4) excellent CSS characteristics. To meet all of these requirements, it is necessary that: (1) a magnetic core is embedded in a non-magnetic slider disclosed in Japanese Patent Laid-Open No. 60-154310, to improve CSS characteristics and to reduce inductance; (2) it has a structure in which a magnetic thin layer can be made as thin as possible to prevent extreme stress from being generated in the magnetic layer and (3); it has a magnetic gap portion without a pseudo-gap effect.
Further, to obtain a high-performance flying-type composite magnetic head, it is important to maintain a stable floating height in the course of the rotation of a magnetic disk.
While the magnetic disk is rotating the air on the surface of the magnetic disk also moves to exert an upward force to a lower surface of the slider. Accordingly, the magnetic head floats from the magnetic disk during the rotation of the magnetic disk. The distance of the magnetic head from the magnetic disk is called a floating height, and the floating height is decreasing year after year because of the increase in recording density of magnetic disk apparatuses. According to Computer Strage Industry Service (Section of Rigid Disk Drive) issued by Dataquest, 1984, pp. 2.2-6, the floating height has reached 10 microinches (0.25 .mu.m). To keep such a submicron floating height stable during the rotation of the magnetic disk, it is necessary that an air-bearing surface of the magnetic head should have good flatness. Since the floating of the magnetic head is obtained by an air flow passing through a gap between the floating surface of the magnetic head (lower surface of the slider) and an upper surface of the recording medium, stable floating cannot be achieved without good flatness of the floating surface of the magnetic head.
In the case of a magnetic head disclosed in U.S. Pat. No. 3,823,416, since the air-bearing surface acting to cause floating is constituted by a single body made of Ni-Zn ferrite or Mn-Zn ferrite, good flatness is easily achieved. However, in the case of a composite magnetic head obtained by embedding a magnetic core in a slit of a non-magnetic slider, fixing the magnetic core with glass and then grinding and polishing its air-bearing surfaces, special attention should be paid to improve tis flatness. This is due to the fact that it is extremely difficult to grind the air-bearing surface to such an extend that the magnetic core and the bonding glass are completely in the same plane as the non-magnetic slider.
In sum, in order to obtain a flying-type composite magnetic head which (1) is capable of performing sufficient recording to a high-coercive force recording medium, (2) has low inductance, (3) high reproduced output and (4) is excellent is CSS characteristics, the first point to overcome is a so-called undulation phenomenon of reproduced output due to the pseudo-gap effect which is caused in a magnetic core having a trapezoidal magnetic gap in which each magnetic core piece has a flat tip portion with a thin magnetic layer coating. The second point to overcome is the deterioration of flatness which may be caused by grinding the air-bearing surface in which the magnetic core is embedded in a slit of the non-magnetic slider and fixed thereto.